Reykjanes Earthquake Swarm: Experts Advise Against Travel To Eruption Site Skip to content

Reykjanes Earthquake Swarm: Experts Advise Against Travel To Eruption Site

By Gréta Sigríður Einarsdóttir

Geldingadalir eruption lava
Photo: Jelena Ciric. Geldingadalir eruption site, July 27, 2021.

On December 21, an earthquake swarm began on the Reykjanes peninsula near the recent eruption site. Around 3,000 earthquakes have been detected every day since, with the biggest measuring 4.9M. Satellite images show a deformation similar to the one preceding the 2021 eruption. 

Slight decrease in seismic activity today

According to natural hazard expert with the Icelandic Meteorological Office Einar Hjörleifsson, 3,300 earthquakes were detected yesterday, but today, there have been slightly fewer tremors detected, 1,300 since midnight. The largest earthquake since midnight was a magnitude 3.6 quake by Kleifarvatn. 

Magma intrusion causes earthquakes

Most of the activity is near the Fagradalsfjall volcano, but earthquakes have also been detected near Grindavík and lake Kleifarvatn. The earthquakes near Grindavík and Kleifarvatn are interpreted as triggered earthquakes due to increased pressure in the ground caused by a magma dike intrusion near Fagradalsfjall. On Christmas Eve, three earthquakes above M4 were detected near Grindavík, the largest one M4.8. There are no signs of magmatic intrusions in other places than by Fagradalsfjall. The earthquake activity by Fagradalsfjall is episodic with periods of very intense earthquake activity.

Deformation similar to events preceding March eruption

Latest InSAR images show clear signs of deformation from 20 to December 26. The deformation seen now is very similar to deformation observed at the end of February this year when a dike intrusion was starting near Fagradalsfjall. This InSAR data supports GPS measurements showing deformation in the same area.

Via the Iceland Met Office

A new eruption?

While no new lava flow has been detected at the crater in Fagradalsfjall for the past three months, there’s still uplift in the area. “It can be difficult to say with some accuracy when an eruption is finished because the volcanic activity can be intermittent, “says coordinator for Volcanic Hazards at the Met Office Sara Barsotti. “As we know from the past, when the peninsula is reactivated, episodic eruptions might occur as a series, “says Sara.

Or more of the same?

The eruption that started on March 19 lasted for about six months. Deformation data show that there is still magma inflow in the crust by Fagradalsfjall, so it is difficult to predict how the situation will evolve. “We continue to monitor the Reykjanes peninsula closely, but we can say that the specific eruption that started on March 19 got to an end. However, even though this episode is closed, we know the activity in the area is still ongoing, and other eruptive phases might start in the near future, “says Sara.

Department of Civil Protection and Met Office urge caution

Due to the elevated seismic activity, the aviation colour code was raised from yellow to orange. The Police’s Department of Civil Protection and Emergency Management has issued an uncertainty warning in the Reykjanes area. Icelandic Met Office experts warn people not to travel in the area because they do not know when or where an eruption might occur or where fissures might open up. The Department of Civil Protection and Emergency Management’s Scientific Advisory Board will meet this afternoon to discuss the situation. 

Waiting game

The activity is similar to events preceding the eruption last March, but experts don’t know when, where, or even if a new eruption will begin. Volcanic tremor pulses often precede eruptions, and such a tremor pulse was detected early on Christmas day but has not been detected since. According to Einar, it might also have resulted from the sheer volume of earthquakes. It is not known when, where, or even if a new eruption will occur, but experts agree that it can’t be ruled out that magma might breach the surface in the Reykjanes area on short notice. 


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